Sample decision on parameter (rails 4)

index.html.erb

<div id="search_block">
  <%= form_tag(action: 'search', method: :put) do %>
    <%= text_field_tag(:search, params[:search], placeholder: 'Search ...') %>
    <%= submit_tag('Go') %>
  <% end %>
</div>
<% if @rentals.blank? %>
  <%# Notify user of missing parameter or empty result set %>
  <h4>Please give a valid search term</h4>
  <div class="help-block">
    <% if @rentals %>
      <%# No results %>
      No rentals found
    <% else %>
      <%# No search term %>
      Please input a valid search term.
    <% end %>
  </div>
<% else %>
  <% rentals.each do |rent| %>
    <%# ... output rent details %>
  <% end %>
<% end %>

search_controller.rb

class SearchController < ApplicationController
  
  def index
    unless params[:search].blank?  # avoid empty or null search parameter
      @rentals = Rentals.where('name LIKE ?', "%#{params[:search]}%")
    end
    @parishes = Parish.all    # using a separate function for a single line is 
    @counties = Counties.all  # just increasing the stack level, doesn't help readability
  end
end

Thanks for the additional details!